The present invention relates generally to electrical machines, and more particularly to a dual-rotor, radial-flux, toroidally-wound, permanent magnet machine.
Electrical machines that transform mechanical energy into electrical energy have been studied, designed and utilized for over a century. Today, electrical machines are widely used in every aspect of human life. Electrical machines may take the form of DC motors or AC motors. DC motors have been in use for a long time due to their high performance in motion and drive applications. With the development of power electronics, new control technology and machine topologies, great progress has been made to replace DC machines in the adjustable speed area with AC motors to obtain better performance, reliability, improved maintenance characteristics, and lower costs. Extensive research and development has gone into developing AC machines that are suitable for drive applications and still match the characteristics of solid state power converters.
AC motors are designed for use with either polyphase or single-phase power systems. AC motors are typically divided into series, synchronous, and induction motors. Induction motors, single-phase or polyphase, the most commonly used type of AC motor, derives its name from the fact that AC voltages are induced in a rotor circuit by a rotating magnetic field of a stator.
Currently, induction machines are the dominant choice for both constant speed and variable speed drives due to the absence of brushes and slip rings. However, induction machines have their drawbacks. Rotor windings are present in all induction machines, rotor current produces rotor resistive losses, decreasing the efficiency of the motor, particularly at low power ratings, and cause cooling problems. Given the excitation penalty of induction machines, permanent magnet machines, in which the air gap flux is established by magnets, have been given attention ever since the Alnico magnet was developed by Bell Laboratories in the 1930's.
With the advent of increased interest in power electronics, Converter Fed Machines (CFM) have been one of the focuses of research and development of electrical machines. Some of the CFMs that have attracted interest include Brushless DC machines (BLDC), Switched Reluctance Machines (SRM), Synchronous Reluctance machines (SynRM), Double Salient Permanent Magnet machines (DSPM), Axial Flux Toroidal Permanent Magnet machines (AFTPM), and Axial Flux Circumferential Current machines (AFCC). However, these all have their own drawbacks and disadvantages.
High torque density and high efficiency are two of the most desirable features for an electrical machine. Improvement of these features have been being one of the main aspects of research on electrical machines in the last couple of decades. The goal of the present invention is to provide an electrical machine having high torque density and high efficiency. Several new topologies have been proposed with improved torque density and efficiency. However, rare earth magnets, i.e., Neodymium Iron Boron (NdFeB), were used in these topologies to keep the efficiency high and achieve the high air gap flux density and high torque density, which causes high material cost. In addition, some topologies are restricted in low speed applications since the losses increase as the speed increases.
Development of a machine topology suitable for moderately high or high speed with high torque density and high efficiency simultaneously using such low cost materials as ferrite magnets is the goal of this invention.
The present invention provides a solution to the above problems by providing a dual-rotor, radial-flux, toroidally-wound, permanent magnet machine that is superior to existing technology because it makes electrical machines having a higher torque density and higher efficiency, so that less materials, smaller volume, lighter mass, and less cost are needed to provide the same output power.